Pressure oxidation process

ABSTRACT

The present invention is concerned with a novel process for the oxidation of metal-sulfur-containing compositions. The invention is particularly concerned with the oxidation of refractory metalsulfur-containing compositions.

United States Patent 'Drobnick et al.

[54] PRESSURE OXIDATION PROCESS [72] inventors: James L. Drobnick,Lakewood; Albert E. Erhard, Denver; Ellsworth W. Daugherty,

Golden, all of Colo. v [73] Assigneez Molybdenum Corporation o1 America,New York, NY.

- [22] Filed: Sept. 11,1969

.[21] Appl.No.: 857,181

[52] U.S.Cl. .23/15 W,23/140, 23/144, 23/224, 23/18, 23/20 [51] Int. Cl...C22b 59/00 [58] Field oISearch .....23/l5,15W,18,19, 224,140, 23/144;75/121 [56] References Cited UNlTED STATES PATENTS 1,118,150 11/1914Robertson ..'...23/15 W 1 Apr. 25, 1972 1/1944 Smith...... ..23/15 WDresher et al., Journal of Metals," June 1956, pp. 794- 800 Usataya,Chemical Abstracts," Vol.47, 1953, p. 5313 Primary Examiner-Herbert T.Carter Attorney-Morgan, Finnegan, Durham and Pine {57] ABSTRACT Thepresent invention is concerned with a novel process for the oxidation ofmetal-sulfur-containing compositions. The invention is particularlyconcerned with the oxidation of refractory metal-sulfur-containingcompositions.

10 Claims, 2 Drawing Figures Patented April 25, 1972 3,658,465

2 Sheets-Shoo. 1

Ppsssums OXIDATION 0F METAL 501. 705 .52 ORR/E5 ,aumu METAL $41.7 0FMETAL 504 F/DE sowr/mv METAL .5 UL F/DE MINERAL ACIDS PREC/P/TA T/ F/LTAA T/ON AIL/(ALI ME TAL SULFA 7E5 H2O PRESSURE OXIDATION 7 OF METALSULF/UE 0X YG'EN OF AIR 5L UARY REC YC'LE SOLUTION F/L TRA Tl ON N 340205005 LEACH F. TRA TION SULFUR CRYSTALL/ZA r/o/v H O CAL CIA/A TIONMETAL 0x105 INVENTORS JAMES L. DROBN/CK ALBERT E. ERHAED BY EZLSWORTHMDAUGHERTY A TTORNE Y5 FIG! Patented April 25, 1972 2 Sheets-Shea. 3

P1255025 OXIDATION OF Aumu METAL 54n- OFMETAL 5ULF/0E 501. ur/a/vsALKAL/ META L SULF/DE .701. U770 AIR PRESSURE OXIDATION OF ALKAL/ METAL.S'AL T OF ME TA L SULF/DE' 50L (IT/01V L/QU/D- 01.10 SULFUR SEPA RAT/ON 50L VENT EXTRACT/0N CRYSTALUZA CAL C/NA 7'ION ALKAL/ METAL SULFATEMETAL OXIDE FIG. 2

IN VENTORS JAMES 1.. DPOBIV/CK LBERT ERHARD y LLSh/OETH M DAUGHEE"nrramvers PRESSURE OXIDATION PROCESS In accordance with the process ofthis invention, a substantial amount of elemental sulfur is obtainedupon oxidation of a metal-sulfur-containing composition in contrast tothe sulfur oxide that normally is obtained with the heretofore 'usedprocesses for the production of metal oxides from compositionscontaining metal sulfides.

The process of this invention comprises subjecting an aqueous systemcontaining a thio derivative of a metal (metal sulfide) under suitableconditions of elevated temperature and pressure in the presence of anoxygencontaining gas so that there results oxidation of the metalsulfide and with the production of elemental sulfur as a by-product. Bysuch process,-oxidation of the sulfur-containing material is effectuatedwithout significant 50, production. 1

The aqueous system treated in accordance with the present invention maybe in the form of an aqueous slurry of a waterinsoluble thio metalcomposition (e.g., water-insoluble molybdenum sulfide) or in the form ofaqueous solutions of water soluble salts of thio metal compositions(e.g., alkali metal salts of molybdenum sulfide).

Prior to this invention there were k'nownprocesses for separatingmetals, particularly refractory metals, from other metals inconcentrates containing said refractory metals and other metals whichcomprise mixing an alkali metal sulfur compound with the concentrate ata molar ratio of alkali metal sulfur compound to refractory metal of atleast 1.5:1, heating the mixture to a fusion temperature of above 700 tol,600 C in a non-oxidizing atmosphere and/or with a reducing agent toobtain a water soluble alkali metal thio-refractory metal sulfurcompound reaction product," (which may be referred to as an alkali metalsalt of a metal sulfide), contacting said product with an aqueous leachsolution and selectively solubilizing said alkali metal thio-refractorymetal compound, and separating said leach solution from a insoluble thepresence of an oxygen-containing gas to effect oxidation ly precipitatea water-insoluble metal sulfide composition. The

resulting mixture is subjectedto filtration to obtain a filtratecontaining alkali metal salts (e.g. alkali metal sulfates) and awater-insoluble metal sulfide precipitate residue. I

An aqueous slurry of the metal sulfide precipitate is then formed by theaddition of water to the water-insoluble metal concentrate residue. Inthe case of certain alkali metal, thiorefractory metal compounds, such,for example, as molybdenum or vanadium-containing, a 'mineral acid maybe added to the leach solution to a controlled pH to selectivelyprecipitate the refractory metal as a water-insoluble metal sulfide." I

In (e.g. above-mentioned known processes, recovered sulfur-containingcompounds are ultimately converted to oxide forms by processes includingthe utilization of a roasting technique by heating ametal-sulfur-containing composition at elevated temperature e.g., 260 to600 C.) in the presence of air. A serious drawback of such a roastingprocedure is that one of the by-products of such roasting is S0 which isof greater concern with respect to air pollution.

Broadly speaking, the present invention relates to a process for thepressure oxidation of a metal-sulfur-containing composition whichcomprises subjecting an aqueous system con taining a thio derivative ofa metal to elevated temperature and elevated pressure in the presence ofan oxygen-containing gas, to effect oxidation of themetal-sulfur-containing composition and produce elemental sulfur, saidaqueous system being selected from the group consisting of aqueoussolutions of water-soluble salts of thio metal compositions and aqueousslurries of water-insoluble thio metal compositions.

The present invention provides a process which avoids the production ofa substantial amount of SO in the manufacture of metal oxides from metalsulfur-containing compounds. lnstead, by the process of the presentinvention, a substantial amount of elemental sulfur is produced in theoxidation of the metal sulfur-containing compound.

Preferably, the pressure-oxidation process of this invention is employedas an intermediate step in an overall process for the recovery of metaloxides from a metal concentrate, the overall process comprising treatingthe metal concentrate to the group consisting of water-insoluble metalsulfides and water-soluble alkali metal thio metal compounds, subjectingan aqueous system containing said metal-sulfur containing composition toelevated temperature and elevated pressure in obtain ametal-sulfur-containing composition selectedfrom sulfide and is putinto-a suitable pressure reactorand pressure oxidized (oxygen on air) atsuitable elevated temperature (e.g., C.) and pressure (e.g., l70p.s.i.g.).

The resulting slurry contains metal oxides and elemental sulfur as thepredominant sulfur component. Advantageously, no significant amounts ofS0 are produced in the above-mentioned pressure oxidation step.

Theabove-mentioned slurry containing the desired metal oxides may thenbe subjected to suitable purification techniques to obtain purifiedmetal oxides. For example, the slurry may be filtered with recycle ofthe filtrate to the pressure reactor and subjecting the residue to anaqueous'ammonia solution to dissolve the metal oxide components. Whenthe resulting mixture is subjected to filtration, a solid sulfur residueis obtained alongv with a filtrate containing soluble metal oxidecomponents. The metal filtrate is then subjected to evaporationresulting in crystallization of the metal oxide components. Thecrystallized metal oxide components are then dried by calcinationresulting in the production of dried metal oxides.

By the overall process shown in FIG. I, it is seen that pure metaloxides may beobtained from metal sulfides with sulfur being produced insubstantial amounts as a by-product instead of SO as is normallyproduced by the known conversion process for obtaining metal oxides frommetal sulfur-containing compositions. 1

The flow sheetshown in FIG. 2 illustrates a process for obtaining metaloxides from aqueous solutions of alkali metal salts of metal sulfideswhich includes a step for the pressure oxidation of alkali metal salt ofmetal sulfide. As shown in FIG. 2, an aqueous solution of an alkalimetal salt of a metal sulfide is charged to a pressure reactor andoxidized in the presence of air or oxygen at elevated temperature andelevated pressure. The resulting mixture is then subjected to aseparation step (e. g., filtration) to give a solid sulfur fraction anda liquid oxidized solution.

The metal component in the oxidized solution is inan oxidized form(e.g., Mo converted to M0 from M0).

The oxidized solution is then subjected to a suitable solvent extractionstep to extract the metal component from the oxidized solution afterwhich the solvent containing the metal component is stripped of themetal component with an aquev ous ammonia solution and evaporated tocrystallize the metal component. The crystallized metal component isthen subjected to calcination resulting in the production of the desiredmetal oxide.

As in the case of the process. illustrated in FIG. 1, the process ofFIG. 2 permits one to produce metal oxides from alkali metal salts ofmetal sulfide solutions without the production of significant amounts ofS0 In carrying out the pressure oxidation process of the presentinvention, the conditions of pressure, temperature and time arecorrelated such that effective oxidation of the metal sulfide (i.e.,water-soluble alkali metal salt of metal sulfide or water-insolublemetal sulfide) is effectuated with the production of elemental sulfurwithout causing significant sulfur oxidation.

If too low a pressure is used, ineffective oxidation of the metalsulfide occurs with resultant poor conversion of the sulfide to anoxidized form. The maximum pressure is of course governed by practicaleconomics and limitations of equipment that is used. It has been foundthat good results are obtained when the pressure is generally in a rangeof 50 to 600 p.s.i.a., and preferably 100 to 200 p.s.i.a.

In like manner, if too low a temperature is employed, poor conversion ofthe metal sulfide to an oxidized form is obtained while the uppertemperature is governed by practical economics and limitations of theequipment that is used. In general, good results are obtained when thetemperature is generally in the range of 60 to 200 C., and preferably105 to 180 C.

Of course, the time required for effecting the desired oxidation variesdepending upon the pressure and temperature conditions. With highertemperature and/or pressure, a lesser period of time is required. Ingeneral, satisfactory yields are obtained when the time period is in therange of minutes to l2 hours, and preferably 1 to 4 hours.

The oxygen required for oxidation may be provided by pure oxygen or air.In order to obtain optimum yields, the amount of oxygen or air that isadded is an amount that is sufficient to provide oxygen up to thesubstantially stochimetric amount for effecting complete oxidation ofthe metal sulfide. If the amount of oxygen that is provided is above thestoichiometric amount, oxidation of the elemental sulfur by productresults which of course is undesirable, while if the amount of oxygen isless than the stoichiometric amount, the extent of oxidation of thesulfide decreases as the amount of available oxygen decreases.

SUITAB LE MATERIALS FOR PRESSURE OXIDATION The following discussiongives details with respect to materials that may be oxidized inaccordance with the process ofthis invention.

Examples of suitable metal sulfur compounds that may be pressureoxidized in accordance with the process of this invention aremolybdenum, vanadium, tungsten, tin and antimonycontaining compounds,all of the aforementioned metals being of the refractory metal type withthe exception of antimony.

The pressure oxidation process of the present invention isadvantageously employed as an intermediate step in an overall processwhereby metal oxides are obtained from metal concentrates.

In such overall process, metal sulfides, either in the form of alkalimetal salts of metal sulfides or in the form of water-insoluble metalsulfides are first obtained from metal concentrates and then the metalsulfide that is obtained, in the form of an aqueous slurry or aqueoussolution, is subjected to pressure oxidation in the manner describedherein. With respect to the first mentioned step, as indicated earlier,metal sulfides may be obtained from appropriate concentrates by mixingan alkali metal sulfur compound with the concentrate at a molar ratio ofalkali metal sulfur compound to metal of at least 1.5:], heating themixture to a fusion temperature of above 700 to l,600 C., in anon-oxidizing atmosphere and/or with a reducing agent to obtain awater-soluble alkali metal salt of metal sulfide. The resulting productis then treated with an aqueous leach solution to selectively solubilizeor leach out the alkali metal salt and the leaching solution containingthe alkali metal salt is then separated from the insoluble concentrateresidue.

In the case of molybdenum, vanadium, tin and antimonycontaining alkalimetal salts of the above-mentioned type, the leach solution containingsaid salt can be treated with a mineral acid to precipitate awater-insoluble acid metal sulfide used in the formation of a slurrythat may be pressured oxidized in accordance with the process of thepresent invention. In the case of molybdenum, vanadium, andtin-containing salt solutions, sufficient acid should be added to theleach solution to lower the pH to less than 8.5 while withantimony-containing leach solutions, the pH should be less than 6.5. Inthe case of tungsten, the water-soluble alkali metal salt of tungstensulfide does not precipitate as a water-insoluble tungsten sulfide.Other means must be used for obtaining the tungsten sulfide inwater-insoluble form which are not economically desirable as far as thepresent overall process is concerned. Thus, as a practical matter whileboth slurries of water-insoluble acid metal sulfides and water solublealkali metal salt of metal sulfide solutions may be convenientlyobtained with molybdenum, vanadium, tin and antimony-containingcompositions for pressure oxidation in accordance with the process ofthis invention, in the case of tungsten, only aqueous solutions ofwater-soluble alkali metal salts of tungsten sulfide are practicallyavailable for pressure oxidation.

Concentrates that may be used for obtaining water-soluble andwater-insoluble metal sulfides to be pressure oxidized in accordancewith our process include refractory metal molybdenum and vanadiumcontaining ore concentrates which also contain impurities such as iron,copper, lead and zinc can be treated in accordance with the presentinvention.

The principle commercially processed and available molybdenum andvanadium ores, in addition to containing the refractory metal, containiron, copper, lead or zinc impurities in the form of water insolublecompounds. The refractory metal sulfide compounds can be concentrated tothe desired degree of concentration by conventional milling andflotation procedures.

The mineral molybdenite, MoS is the principal commercial source ofmolybdenum. This mineral is normally found in ores in amounts of 0.2 to1 percent by weight of the ore. The normal impurities associated withmolybdenite are relatively large amounts of SiO pyrite, FeS andchalcopyrite, CuFeS. and lesser amounts oflead and zinc sulfides.

Another commercial source of molybdenum is the byproduct from acopper-molybdenum ore concentrate processed to recover copper values.

A commercially available molybdenum ore concentrate containing about 58percent by weight molybdenite, MoS. and a commercially availablecopper-molybdenum ore concentrate by-product having about 70 percent byweight molybdenum sulfide have the following compositions:

MoS, Cu-MOS ore byore Wt. product Wt. 92 M08 58.l 70.0 Fe 5.3 6.0 Pb0.85 0.20 Cu 0.46 8.0 lnsol. 20.5 6.0

A principal source of vanadium sulfide is the mineral patronite, V 5Patronite ores contain about I percent vanadium. A by-product source ofa vanadium-containing concentrate is known as ferrophosphorous which isobtained during elemental phosphorous production. The principalcontaminants are iron, chromium and phosphorous.

A principal commercial source of tungsten is the mineral scheelite, CaWOThe commercial ores in addition to CaWO,, contain relatively largeamounts of silica and lesser amounts of pyrites, FeS PbS, and CuS, anddepending on the ore source, varying amounts ofzinc and lead impurities.

Another source oftungsten is the mineral tungstenite WS The principalcommercially processed and available tin ore concentrates contain tinoxide, iron, arsenic, lead and zinc impurities in the form of waterinsoluble compounds. The tin oxide can be concentrated to the desireddegree of concentration by conventional milling and flotationprocedures.

The mineral casserite, SnO is the principal commercial source of tin.This mineral is normally found in ores in amounts of L5 to 5 percent byweight of the ore. The normal impurities associated with tin oxide arerelatively large amounts ofiron and lesser amounts of arsenic, lead, andzinc.

EXAMPLE c An'aqueous leach solution was obtained in the manner reportedabove in Example A and contained about 26.85 g/l of molybdenum in theform of water soluble sodium thio-molybdate and had an initial pH of 10to 12 and was acidified by the addition thereto of 37 l-lCl. Asufficient amount of HCl was that may be pressure oxidized in accordancewith our invention. 1 1

Examples 1 and 2 illustrate pressure oxidation of an aqueous slurry of awater-insoluble metal sulfide while 3 and 4 relate to pressure oxidationof an aqueous solution of an alkali metal salt of metal sulfide.

EXAMPLE A Four thousand pounds of molybdenite, M05 ore concentrateobtained from a commercial milling and flotation procedure is used asfeed to the process. The molybdenite concentrate has the followingprincipal constituents:

7: by Weight M08 70.0 CuS 6.0 ZnS 2.5 FeS 3.0 PbS 1.5 Acid lnsol. l5.0

The ore concentrate is admixed with 10,000 lbs. of anhydrous sodiumsulfate and 2,680 lbs. of anhydrous of potassium sulfateand"2,400 lbs.of ground coke. This represents a molar ratio of ingredients ofapproximately 2.8 N21 SO :0.7 X 8058 C: 1 MoS The admixture was fed to afurnace and heated to a temperature of 850 to 950 C. and maintained inthis temperature range for about 30 minutes. At this temperature themixture fuses and becomes molten. The liquidmass is cast and allowed tocool.

The cool mass weighing about 8,400 lbs., evidencing about 50 percent by.weight loss of principally CO was ground to a particle size of less than10 mesh and fed to a leach tank. The ground reaction product iscontacted with about a 3:1 ratio by weight of aqueous leach-solution andagitated for about 1 hour at about 35C. to extract substantially all ofthe water soluble alkali metal thio-molybdate compound. v

The leach liquor is separated from the water insoluble residue. Theresidue is washed and the washed liquid is added to the leach liquor.The combined liquor has a pH of about .10 to 12 and contains about 60g/l of the water soluble alkali metal thio-molybdate, measured asmolybdenum, and substantially no PbS, CuS, ZnS or FeS since thesecompounds are not water soluble and do not form water soluble alkalimetal thio-compounds.

The water insoluble residue contains substantially all of the PbS, CuS,ZnS and FeS, the unreacted carbon and the remaining gangue.

This residue can be dried and treated to recover copper, lead and/orzinc values.

EXAMPLE B The aqueous leach liquor of Example A containing the watersoluble alkali metal thio-molybdate can then be acidified by theaddition thereto of a sufficient amount of sulfuric acid to lower the pHto about 2.5. As the pH is lowered, starting at a pH of about 6, a waterinsoluble acid molybdenum sulfide is formed and starts to preciptiatefrom solution. At pH 2.5 substantially all of molybdenum sulfidecompound has precipitated. The precipitate is washed, dried and heatedin an inert atmosphere to a temperature of 600 C. to drive off exces'ssulfur as elemental sulfur.

The remaining solid is analyzed and found to contain 99.5 percent byweight of MoS.

added to reduce the pH to 1.0. During the addition of HCl a brownmaterial precipitated from solution. The precipitate was separated fromthe leach solution, washed thoroughly and dried.

The dried precipitate was analyzed and found to bean acid molybdenumpolysulfide having the following compositions:

7: by weight Mo 33.65 S 64.48 Na 0.099

The amounts of excess sulfide in the precipitate varies with the amountof sulfide in solution at the point of precipitation.

The precipitate was heated in an inert atmosphere at a temperature below600 C. and sulfur was distilled.

The temperature was then gradually increased over a period of 40 minutesfrornabout 315 to 540 C. and no additional sulfur volatized. The residueappeared to be M08 and when analyzed was found to contain 40 percent bywt. sulfur.

EXAMPLE D An aqueous leach solution was obtained in the manner reportedin the (Example A) and contained about 12.8 grams per liter ofmolybdenum in the form of sodium thio-molybdate and had aninitial pH ofl2.0 and was slowly acidified by the addition thereto of sulfuric acidto obtain a pH of 1.0.

The sulfuric acid was added to various hydrogen ion concentrations,during which the entire system was agitated. Samples of the slurry wereextracted and filtered at the indicated hydrogen ion concentrations. Thefiltrate was analyzed for molybdenum concentration and the followingresults were obtained.

Effect of pHon Molybdenum Solubility in a Sodium Thiomolybdate-SodiumSulfide Sodium Sulfate-Potassium Sulfate System Slurry Mo Analysis of pHFiltrate g/l 12.0 12.80

An analysis of the dried precipitate was also carried out and theresults obtained are reported below.

Element 71 Mo 33.7 S 64.5 Na 0.l

The ratio of molybdenum to sulfur indicates that an acid molybdenumpolysulfide precipitate was obtained.

EXAMPLE 1 Example Illustrating Pressure Oxidation of MolybdenumPolysulfide Employing Compressed Air Element 71 Mo 33.7 S 64.5

A slurry consisting of 1.6 liters at 5.8 percent solids was transferredto a l-gallon agitated pressure reactor (Pfaudler), heated to 160 C. andthen pressurized to 170 p.s.i.g. by introducing compressed air to thereactor. The oxidation reaction was obviously progressing, since thepressure increased to 400 p.s.i.g. after 1 hour of agitation, indicatingan exothermic reaction. The pressure was released to 90 p.s.i.g. andimmediately repressurized to 370 p.s.i.g. by introducing additionalcompressed air to the reactor to obtain oxygen from the air, and thenallowed to react for approximately 1 hour. This pressure release andrepressuring technique was employed for an additional three times toinsure that sufficient oxygen was available for quadravalent molybdenumoxidation.

The entire system was allowed to cool to room temperature before thematerial in the reactor was discharged. The resulting slurry wasfiltered for solid and solution separation. The filter cake had agrayish texture. Analysis of the oven dried (480 F.) filter cake was asfollows:

Element 7:

Mo 39.7 S 36.2 (Carbon disulfide dissolution method) S 37.6 (Lecovolatilization method) The filtrate pH was 0.8.

A sample of the dried filter cake was leached with an ammonium hydroxidesolution (29 percent) at 60 C. for minutes to determine the molybdenumsolubility. The molybdenum solubility was 98.9 percent and the remainingresidue weight calculated to 36 7: S, indicating that asulfur-molybdenum separation can be achieved by this technique.

The carbon disulfide dissolution data indicate the sulfur present in thereactor discharge is predominately elemental sulfur.

EXAMPLE 2 EXAMPLE ILLUSTRATING PRESSURE OXIDATION OF MOLYBDENUMPOLYSULFIDE EMPLOYING OXYGEN This experiment illustrates the batchslurry oxidation of water and molybdenum polyslufide with oxygen undervarious conditions of temperature, pressure, and time. A 2-liter Parr4500 series pressure reactor was employed for this experimental work.The molybdenum polysylfide employed was the same as that used in Example1 (Le. metal sulfide of Example D).

Oxygen was introduced to the pressure reactor under pressure after thedesired temperature had been attained. The oxidation reaction wasallowed to proceed until a sample taken from the reactor was in the pHrange of pH 0.9 to pH 0.8, after which the pressure reactor was allowedto cool and subsequently transferred to a filter where the solids wereseparated from the solution. The solution was analyzed for molybdenumcontent and the efficiency of molybdenum precipitation calculatedaccordingly.

The solids were dried, analyzed and mixed with an aqueous ammoniasolution to dissolve the molybdenum values from the sulfur contaminants.The aqueous ammonia leach solution was filtered for a liquid-solidsseparation. A qualitative test of the solids indicated that the solidswere substantially elemental sulfur.

The data obtained from the above experiment presented in the tablebelow. It appears that the retention time at the conditions employed areless than 12 hours and the pH of the oxidized slurry must be less thanpH 3.0. The optimum pressure and temperature relationships are dictatedby the economics involved, e.g., less retention time will be required atthe high pressures and temperatures.

Experiment A B Reaction Temperature C. 150 220 Total psia 1 14.6 466.6

O psia 102.6 189.9 Reaction Time hours 12.5 2.0 Reacted Slurry pH 1.02.8 Dried Precipitate Analysis 7: Mo 38.4 28.7 Mo Precipitated 7c 91.660.4 Mo Soluble in Aqueous Ammonia Solution 71 97.4 99.0

EXAMPLE 3 EXAMPLE ILLUSTRATING PRESSURE OXIDATION OF SODIUMTHIOMOLYBDATE BATCH OPERATION This example relates to batch oxidation oftetravalent molybdenum in solution as sodium thiomolybdate employingvarious conditions of temperatures, oxygen over pressure, time andmixing. A 2-1iter Parr pressure reactor provided with externalelectrical temperature control and intake ports for air or oxygen, aswell as a sampling port, was used for carrying out the pressureoxidation.

The pressure reactor was charged with 500 ml. of the aqueous solution ofalkali metal salt of metal sulfide (sodium thiomolybdate) prepared inaccordance with the method reported in Example A.

The conditions for all experiments were the same, except for reactionconditions, and are listed as follows:

Temperature 170C. Total Psia 164.6 Steam Psia 1 14.8 0 Psia 49.8

Complete oxidation was measured by observing the color of the oxidizedproduct, which was green, at a pH of pH 2.0 to 2.4. A blue colorindicated incomplete oxidation.

Experiment A B C D E Agitator tip speed ft/min 376 1120 1120 376 1120Retention Time to pH: 2.0-2.4 minutes 42 32 15 110 45 Mo Analysis ofSodium Thiomolybdate Solution g/l Mo 20.0 153 20120.1 41.6 40.0

Percent elemental sulfur Recovered from oxidized Solution as related toM0 in system (S/MoX 50.2% 49.0% 37.9% 48.1%

48.8% Mo Content of Sulfur: 7: Mo 0.74 0.36 0.11 0.13 0.19 SulfurPurity: 71 90.3 92.1 97.2 94.4 91.8

The test data reported above shows that oxidation of tetravalentmolybdenum can be accomplished with the formation of elemental sulfur.The quantity of elemental sulfur formed varies with the conditionsemployed. The data also shows that the effect of mixing greatly enhancesthe time necessary for oxidation.

EXAMPLE 4 EXAMPLE ILLUSTRATING PILOT PLANT PRESSURE OXIDATION OF SODIUMTHIOMOLYBDATE AND SOLVENT EXTRACTION PURIFICATION (CONTINUOUS OPERATION)A solution prepared in accordance with the method of Example A andcontaining 25 g/l Mo at a pH of 12.5 was continuously fed to the firstoxidation reactor at a rate of 0.4 gpm. The pressure and temperature ofthe vessels throughout the What is claimed is:

l. A process for pressure oxidation of a metal-sulfide compound selectedfrom the group consisting of molybdenum sulfide, vanadium sulfide,tungsten sulfide, tin sulfide, antimony l-S-hour run were as follows:sulfide and the alkali metal salts thereof which comprises subjecting awater solution or a water slurry of said metal sulfide p or compound toa temperature of from about60 to 200 C. and oxidation vessel No 1 2'5352440 a pressure of from about 50 to about 600 p.s.i.a. in theoxidation vessel 2 150 320 presence of oxygen or air in an amountsufficient to produce Sulfur Recovery Vessel 32-60 270 elemental sulfurto effect oxidation of the metal sulfide comk 3240 240-260 pound andproduce elemental sulfur. I

v 2. A process according to claim I wherein the metal sulfide Samplestaken from. oxidation vessel commencing at 9 Compound is water'insPlublemqlybdenum hours of operation w f th oxidized with 3 percent 3. Aprocess according to claim 1 where n the metal sulfide hydrogen peroxideat 70 C. to obtain data as to complete oxcompound sF' metal f b idation.l00-ml. samples, were used for this analysis. The A f accordmg wheremthe P Sulfide hydrogen ion concentration (PH) f the solution Sampledcompound rsawater-soluble alkali metal salt obtained by mixfromoxidation vessel No. 2 ranged from pH 2.5 to pH 2.65. mg an dlkah 'TSulfur compound i a concentrate The solution was green in color,indicating efficient oxidation. a molar ram) L5 to fl w" the qg a fHydrogen peroxide data following also indicated that the solutemperaturef 700 to L600 a non-ox on was oxidized mosphere, contacting said productwith an aqueous leach solution and selectivity solubilizing said alkalimetal salt and separating said leach solution from an insolubleconcentrate lb H 0 for Complete residueoxidation 5. A process for thepressure oxidation of a metal sulfide "Ours opemon 3 0006 selected fromthe group consisting of molybdenum sulfide, 1| vanadium sulfide,tungsten sulfide, tin sulfide, antimony sul- 12 0.0036 fide and thealkali metal salts thereof which consists essen- 09024 tially ofsubjecting a water solution or a water slurry of said :2 metal sulfideto a gas selected from the group consisting of air and oxygen in anamount sufficient to produce elemental sulphur at a temperature of fromabout 60 to about 200 C. Sulfur discharged from the sulfur recoveryvessel appeared and a pressure of from about'50 to about 600 p.s.i.a. toeffect quite yellow in color, indicating high purity. The analysis ofthe oxidation of the metal sulfide and produce elemental sulthis sulfursample was as follows: fur.

, 99.8 71 S 6. A process according to claim 5 wherein the metal sulfide0.17 M0 is molybdenum sulfide or the alkali metal salts thereof. Theoxidized solution was clarified and fed to a solvent ex- 7. A processaccording to claim 5 wherein the metal sulfide traction circuit forpurification and separation of sodium and is vanadium sulfide or thealkali metal salts thereof. potassium sulfate. 40 8. A process accordingto claim 5 wherein the metal sulfide The solvent extraction circuit,consistedof three extraction is tin sulfide or the alkalimetal saltsthereof. stages, two sulfate scrubbing stagesand three stripping stages.9. A process according to claim 5 wherein the metal sulfide A flowdiagram of this system follows: in antimony sulfide or the alkali metalsalts thereof.

25 gJl. Mo Feed 40 gJl. NaOH 76 g./l. NH; pH 2.5 0.06 g.p.m. Solution M00.4 g.p.m. 0.1 g.p.m. I No Stripped Stripped Tertiary Tertiary AmineExtraction l Scrub Stripl-wAmine Solvent Section Section Section (out)(In) 1 2 3 4 5 0 7 8 1 Purified Raflinate Ammonium 0.06 g./l. MoMolybdate pH 3.0 Solution to 0.45 g.p.m. Evaporation 100 g./l. Mo A 0.1g.p.m.

. The extraction of molybdenum from the oxidized solution 10. A processfor the pressure oxidation of an alkali metal was greater than 99percent. Product analysis of the salt of a metal sulfide selected fromthe group consisting of evaporated ammonium molybdate solution aftercalcination at molybdenum sulfide, vanadium sulfide, tungsten sulfide,tin 450 C. for final sulfate removal was as follows: sulfide andantimony sulfide, which comprises subjecting a water solution of saidmetal sulfide to a gas selected from the Constituent group consisting ofair and oxygen at a temperature of from Mo 99.0 about 60 C. to about 200C. and a pressure of from about 50 E 885 to about 600 p.s.i.a. to effectthe oxidation of the metal sulfide 0:004 and produce elemental sulfur. S0.03 l= i

2. A process according to claim 1 wherein the metal sulfide compound is water-insoluble molybdenum sulfide.
 3. A process according to claim 1 wherein the metal sulfide compound is a water-soluble alkali metal thio-molybdate.
 4. A process according to claim 1 wherein the metal sulfide compound is a water-soluble alkali metal salt obtained by mixing an alkali metal sulfur compound with a metal concentrate at a molar ratio of at least 1.5 to 1, heating the mixture to a fusion temperature of 700* to 1,600* C. in a non-oxidizing atmosphere, contacting said product with an aqueous leach solution and selectivity solubilizing said alkali metal salt and separating said leach solution from an insoluble concentrate residue.
 5. A process for the pressure oxidation of a metal sulfide selected from the group consisting of molybdenum sulfide, vanadium sulfide, tungsten sulfide, tin sulfide, antimony sulfide and the alkali metal salts thereof which consists essentially of subjecting a water solution or a water slurry of said metal sulfide to a gas selected from the group consisting of air and oxygen in an amount sufficient to produce elemental sulphur at a temperature of from about 60* to about 200* C. and a pressure of from about 50 to about 600 p.s.i.a. to effect the oxidation of the metal sulfide and produce elemental sulfur.
 6. A process according to claim 5 wherein the metal sulfide is molybdenum sulfide or the alkali metal salts thereof.
 7. A process according to claim 5 wherein the metal sulfide is vanadium sulfide or the alkali metal salts thereof.
 8. A process according to claim 5 wherein the metal sulfide is tin sulfide or the alkali metal salts thereof.
 9. A process according to claim 5 wherein the metal sulfide in antimony sulfide or the alkali metal salts thereof.
 10. A process for the pressure oxidation of an alkali metal salt of a metal sulfide selected from the group consisting of molybdenum sulfide, vanadium sulfide, tungsten sulfide, tin sulfide and antimony sulfide, which comprises subjecting a water solution of said metal sulfide to a gas selected from the group consisting of air and oxygen at a temperature of from about 60* C. to about 200* C. and a pressure of from about 50 to about 600 p.s.i.a. to effect the oxidation of the metal sulfide and produce elemental sulfur. 